The present invention relates to an object recognizing device which is capable of recognizing an object by transmitting light from a light source and receiving reflected light from the object.
FIGS. 4 and 5 show a conventional laser radar (pulse radar) unit 4 comprising a semiconductor laser (light source) and a light sensor (photodiode), which is attached to a vehicle 5 for recognizing an object on the road ahead of the vehicles In FIGS. 4 and 5, numeral 41 designates a lens disposed at a radiation outlet of the laser light source and numeral 42 designates a lens disposed at a reflected light receiving port of the light sensor. The laser radar of this type can recognize a distant object at a distance of not less than 100 m therefrom if the monitored space does not contain aerosol such as fog, smoke and dust. But, its ability may be extremely reduced if there is aerosol that scatters light radiation emitted to the object and reflected light therefrom.
Japanese laid-open patent No. 6-215300 discloses another conventional object-recognizing device that recognizes an object in an area ahead of the vehicle through video taking by a video camera mounted on the vehicle.
This device, however, is not usable in poor visibility conditions, e.g., in fog, because the video camera cannot monitor the forward area even when illuminated by the headlights of the vehicle.
In case that, as shown in FIG. 12, the headlights 10 of a vehicle 13 on a road 14 illuminate a forward area with light LL at a relatively large divergence angle 8 and a video camera 8 takes a reflected light (RL) image of the illuminated area, but aerosol Z (fog, smoke or dust) contained in the air space of the illuminated area may scatter the light LL and then the light N of the scattered light enters as a noise signal into the video camera 8. A part of light LL passing a layer of aerosol Z illuminates an object 9 in the illuminated area and reflected light RL therefrom is further scattered by aerosol Z and attenuates. As a result, a very small part of reflected light RL reaches the video camera.
The more aerosol particles Z that are contained in the illuminated space, the more the noise increases and the less the reflected light RL reaches therefrom. Consequently, the video camera 8 cannot take an image of the forward area through the aerosol layer even when the area is illuminated with light LL of an increased intensity.
Japanese laid-open patent No. 54-92117 also discloses such a device that recognizes an object in a forward area by taking an image thereof with an infrared camera attached to a vehicle.
Although the infrared camera can well recognize such an object that emits a large amount of infrared radiation (e.g., a human body, car and so on) even at night or in fog, it may not clearly indicate a road surface, road construction or other object that emits a small amount of infrared radiation. For example, the infrared camera cannot detect a white line marked on a road surface.
The problems to be solved are as follows:
The conventional laser radar cannot recognize an object in a monitored area if there is an excess of aerosol such as fog, smoke and dust particles that may scatter laser light.
The conventional object-recognizing device using a video camera cannot take a forward area image in a foggy, smoky or dusty atmosphere.
The conventional object-recognizing device using an infrared-camera cannot recognize an object that emits a small amount of infrared radiation.